1. Field of the Invention
This invention relates to an original reading apparatus in which the images formed by lights of different colors of an original are converted into electrical signals.
2. Description of the Prior Art
Original reading apparatus are used in transmitters of facsimile or image processing apparatus such as image editing apparatus. Heretofore, in reading the image of a multicolored original, light has been applied to the original from a light source such as a halogen lamp or the like, the reflected light from the original has been passed through an imaging lens to color resolving means such as a dichroic mirror or the like, the light has been resolved into lights of a plurality of wavelength ranges by the color resolving means and imaged on light-receiving elements such as linear solid image pick-up elements.
FIG. 1 of the accompanying drawings shows an example of the construction of such a reading apparatus of the prior art. In FIG. 1, reference numeral 1 designates an original table on which an original 12 is placed, and reference numeral 2 denotes a bar-shaped light source such as a halogen lamp or a fluorescent lamp. The light source 2 is mounted in a reflector 3. Reference numerals 4, 5 and 6 designate a first, a second and a third reflecting mirror. The first reflecting mirror 4 scans the original 12 (minor scanning) while being moved with the light source 2 in the direction of arrow A along a guide rail, not shown. The second mirror 5 and the third mirror 6 are made integral by a support, not shown, and are moved on the aforementioned guide rail in the same direction B as the direction of movement of the first mirror 4 at one half of the movement velocity of the first mirror 4. By this, the length of the optical path between the original 12 and an imaging lens 7 is maintained constant. The light beam from the original passed through the mirrors 4, 5, 6, a filter 13 absorbing green light and transmitting lights of red and blue wavelength ranges therethrough, and the lens 7 in the named order enters a dichroic mirror 8 disposed rearwardly of the lens 7. In this example, the dichroic mirror 8 reflects red light and directs it to a linear solid image pick-up element, for example, a CCD 9, and transmits blue light and directs it to a linear solid image pick-up element, for example, a CCD 10. Accordingly, the image of the original 12 by red light is formed on the CCD 9 and the image of the original 12 by blue light is formed on the CCD 10. The CCDs 9 and 10 have a number of picture elements (point-like unit areas which convert light into an electrical signal) in the major scanning direction (the direction perpendicular to the plane of the drawing sheet of FIG. 1). As is well known, when the CCDs are driven, electrical signals are taken out from a number of picture elements in succession from the end thereof and a time-serial signal corresponding to the image is formed. Accordingly, by reading out the signals from the light-receiving elements such as CCDs 9 and 10 in good order (major scanning) during minor scanning, there can be obtained successive signals which have raster-scanned the original 12. The CCDs 9 and 10 read the same position of the original. Designated by 14 is a housing which contains these members therein. The lamp 2 and the mirrors 4, 5, 6 move forward to positions designated at 2', 4', 5' and 6', respectively, and then move to their respective home positions.
FIG. 2 of the accompanying drawings shows another example of the reading apparatus according to the prior art. In this example, the original is moved and scanned and the image information thereof is color-resolved into three colors, i.e., red, blue and green. In FIG. 2, reference numeral 21 designates original feeding rollers which support and slidably transport the original 12 on a platen glass 23 in the direction of arrow C. The light from a light source 15 is reflected from the original at a position P and is caused to enter an imaging lens 7 via a first mirror 16. Further, red light is reflected by a dichroic mirror 8 and a light including blue and green lights is transmitted therethrough. The transmitted light is caused to enter a dichroic mirror 17. The dichroic mirror 17 reflects blue light and transmits green light therethrough. Accordingly, the red light, the blue light and the green light are received by CCD 9, CCD 10 and CCD 11, respectively. Designated by 22 is a plate for holding down the original against the glass 23 to enable the original to be well imaged on the CCDs 9, 10 and 11.
In the above-described apparatus of the prior art, a number of means for color-resolving light corresponding to the number of image pick-up elements used are disposed only rearwardly of the lens system. Accordingly, to secure a space in which the color resolving means are disposed, a lens system having a long focal length must unavoidable be employed as the lens system, and this has led to an increased length of the optical path forward of the lens system and has prevented the apparatus from becoming compact.